I don't know which book was recommended because I didn't spot it in the replies above but I recommend "
Secrets of the Baby Whisperer" by Tracy Hogg if you haven't read it already. I wish I had read that book prior to giving birth--it's definitely not a "cure-all" but it really helped my husband and I develop a plan--we read it when my son was about 4 months-old.
Personally, I found that the total CIO method only backfired on us and set us up for more trouble getting our son to sleep. It terrified him to be left to cry for long periods of time and he got panicky. So, gradually we have helped him develop more independence when it comes to sleep times. My son is eight-months-old now and he is at least 30 pounds (he was already 7 kilos when he was 4 months old!)--he's a very strong and tall baby--he is already starting to walk (started about a month ago) and can say a few words and phrases in both English and Cantonese (my husband is Chinese and I'm white). So, for us, packing him around and rocking him (especially since I have a herniated disc in my back) was not an option beyond 3 or 4 months.
I found that by establishing a routine for sleep times it has helped--at night, my son gets a bath from his dad when he comes home from work. Then after that he gets a bit of free time to play in the living room--usually his dad is tossing him up and catching him--then I take him into his room and we sit in a chair with a little lamp on and I read books to him--he is pretty wiggly so something he's not that interested but some books he really likes. After that I have a bottle ready for him and I feed him and sing to him and usually he falls asleep. But now that he is getting so big and tall, I just lay a pillow across my lap and let him lay on the pillow with his feet propped up against my stomach and I feed him--and then if he's still not asleep, I sway him back and forth using the motion of my knees. Sometimes just before he falls asleep, I put him in his crib and let him nod off. Recently he has started initiating naptimes more on his own which is good. We rarely deviate from this routine so our son is secure because he already knows what's coming next in his day.
I think that the book I recommended is good because it helps you kind of pinpoint what personality type your baby has and from there it's easier to come up with a strategy. Routine and strategy are really lifesavers, though.